Expression of engrailed can be lost and regained in cells of one clone in crustacean embryos.

In three species of higher crustaceans (Malacostraca) the expression of engrailed has been analysed in relation to the development of the cell division pattern in the germ band. The species differ in the timing of initial en expression. Compared to Cherax destructor and Neomysis integer the onset of en expression in Orchestia cavimana is delayed and appears one cell cycle later. In Cherax and Neomysis cells of the posterior margin of early en stripes lose en expression. This phenomenon does not occur in Orchestia. In a second step the en stripes widen both by division of en positive cells and de novo expression at the posterior margin of the en stripes. The widening phase is similar among all investigated species. In Cherax and Neomysis the cells with de novo en expression are derivatives of cells, which have ceased to express en one cell cycle before. The results in higher crustaceans suggest that neither initiation nor maintenance of en expression is controlled by lineage restrictions and that early en expression is not clonally transmitted. Furthermore, some aspects of boundaries and fields in embryos are discussed.